November 14, 2013

Approaching Comets ISON And Encke Pose For NASA’s MESSENGER

NASA’s MESSENGER spacecraft helped snag a few images of comets ISON and Encke as they are making their way closer to Mercury and the Sun, where they will be much brighter and more readily visible to amateur astronomers.

Comet ISON was discovered in September 2012 by amateur astronomers in Russia using a 16-inch telescope that is part of the International Scientific Optical Network. Astronomers predict ISON will be flying within 700,000 miles of the Sun’s photosphere on November 28, after which it could either become a great spectacle for backyard astronomers or disintegrate completely.

MESSENGER is a Mercury-orbiting spacecraft that has been given the task of collecting observations of ISON for the next several weeks. NASA said from November 9 through November 11, the probe’s Mercury Dual Instrument System (MDIS) helped to capture its first images of the comet.

"We are thrilled to see that we've detected ISON," Ron Vervack of the Johns Hopkins University Applied Physics Laboratory (JHUAPL), who is leading MESSENGER's role in the ISON observation campaign, said in a statement. "The comet hasn't brightened as quickly as originally predicted, so we wondered how well we would do. Seeing it this early bodes well for our later observations."

Comet ISON is not the only comet MESSENGER has been able to pick up during observations. NASA said from November 6 through November 8 the spacecraft’s imagers helped to pick up its first photographs of comet Encke. This comet has been known of since its discovery in 1786, although it wasn’t recognized as a periodic comet until 1819.

Comet Encke has an orbital period of 3.3 years, which is the shortest period of any known comet. November 21 will mark Encke’s 62nd recorded perihelion.

"Encke has been on our radar for a long time because we've realized that it would be crossing MESSENGER's path in mid-November of this year," Vervack said. "And not only crossing it, but coming very close to Mercury."

He said early images of both comets are just a few pixels across, but MESSENGER will have more opportunities to snap better photos in the upcoming week as the comets make their closest approach to Mercury.

NASA said on November 18, Encke will travel within just 2.3 million miles of Mercury. If the comet was to come this close to Earth it would rank as the third closest approach of a comet to our planet. ISON will be passing within 22.5 million miles of Mercury on November 19, just a little over a week shy of its upcoming close brush with the sun.

"By next week, we expect Encke to brighten by approximately a factor of 200 as seen from Mercury, and ISON by a factor of 15 or more," Vervack said. "So we have high hopes for better images and data."

Three of MESSENGER’s instruments, including MDIS, the Mercury Atmospheric and Surface Composition Spectrometer, and the X-Ray Spectrometer, will be keeping their sights on the two comets, collecting as many observations as possible. Vervack said there are a few issues that could impact the volume of data MESSENGER is able to gather. He said for the health of the spacecraft, portions of each orbit must be spent in a thermally safe mode, which precludes gathering data over the entire orbit.

"We can't fill up the spacecraft recorder with comet data because doing so could cause a backlog that impacts our primary mission of collecting observations from Mercury," he said.

However, the MESSENGER team said they are optimistic things will go as planned, assuming the comets hold up their end of the bargain.